Mounted planar filament

This application claims priority to US Provisional Patent Application No. U.S. 63/579,091, filed on Aug. 28, 2023, which is incorporated herein by reference.

The present application is related to x-ray sources.

X-rays have many uses, including imaging, x-ray fluorescence analysis, x-ray diffraction analysis, and electrostatic dissipation.

A large voltage between a cathode and an anode of the x-ray tube, and a heated filament at the cathode, can cause electrons to emit from the filament to the anode. The anode can include a target. The target can generate x-rays in response to impinging electrons from the cathode.

The following definitions, including plurals of the same, apply throughout this patent application.

As used herein, the terms “on”, “located on”, “located at”, and “located over” mean located directly on or located over with some other solid material between. The terms “located directly on”, “adjoin”, “adjoins”, and “adjoining” mean direct and immediate contact.

As used herein, the term parallel means exactly parallel; parallel within normal manufacturing tolerances; or almost exactly parallel, such that any deviation from exactly parallel would have negligible effect for ordinary use of the device.

As used herein, the term “x-ray tube” is not limited to tubular/cylindrical shaped devices. The term “tube” is used because this is the standard term used for x-ray emitting devices.

An x-ray tube can include a filament for emission of electrons. A planar filament can be preferred for focusing the electron beam to a circular spot. It can be difficult, however, to place the filament repeatedly in the appropriate location.

Failure to align the filament within a cathode cup, in every x-ray tube manufactured, can result in undesirable variance in x-ray spot location between different x-ray tubes.

Planar filaments can twist or warp. This can adversely affect the electron beam shape and focusing.

Placing a tiny filament on electrodes can be difficult for operators, and can result in variation between different x-ray tubes. Welding the filament to electrodes can result in overheating of the filament or surrounding material, which can further warp or damage the filament or other material.

A weld beneath the filament can be difficult or impossible to inspect. Without proper inspection, x-ray tubes that lack a properly welded filament can be sold and installed in expensive equipment. Improperly welded filaments can result in early failure of the x-ray tube, and of the tool which uses the x-ray tube.

A filament can emit electrons in all directions. A planar filament typically emits electrons in a desirable direction, towards the anode target, from a top side of the planar filament that faces the target. The planar filament also can emit electrons in an undesirable direction, towards a cathode cup, from a bottom side of the planar filament. The bottom side is opposite of the top side. The electrons from the bottom side can change direction (e.g. about 180°), due to a negative voltage of the cathode cup, pass between filament wires, and emit towards the target. These electrons from the bottom side are not focused properly. Therefore, the bottom side electrons can result in a misshaped electron spot at the target.

The filament assembliesdescribed herein can solve the previously noted problems. Each embodiment can solve one, some, or all of these problems.

As illustrated in, a filament assemblycan include a filamentand a pair of collector plates Cand C. The collector plates Cand Ccan provide support for the filamentand reduce twisting or warping of the filament.

The filamentcan consist of or can include an elongated wire extending, non-linearly in a plane (parallel with the sheet of the paper in, or planein), between a first end Eand a second end Eof the filament. A planar dimension of the pair of collector plates Cand Ccan be located in this plane.

A top sideof the pair of collector plates Cand Cand of the filamentcan be aligned and co-planar with each other. The top sidecan face the target().

A bottom sideof the pair of collector plates Cand Cand of the filamentcan be aligned and co-planar with each other. The bottom sidecan face away from the target(). The bottom sidecan be opposite of the top side.

The top sidecan be aligned with a top plane. The bottom sidecan be aligned with a bottom plane. The top planecan be parallel to the bottom plane. A thickness of the pair of collector plates Cand Ccan equal a thickness of the filament. The thickness can be measured perpendicularly to the plane.

The pair of collector plates Cand Ccan be separated from each other (i.e. not directly touch, not adjoin). The pair of collector plates Cand Ccan be electrically coupled to each other by the filament. The filamentcan be the only structure that is in an electrical circuit between the pair of collector plates Cand C.

The pair of collector plates Cand Ccan include a first collector plate Cand a second collector plate C. The first collector plate Ccan be electrically-coupled to the first end Eof the filament. The first collector plate Ccan adjoin the first end Eof the filament. The second collector plate Ccan be electrically-coupled to the second end Eof the filament. The second collector plate Ccan adjoin the second end Eof the filament.

As illustrated in, an outer perimeter Oof the first collector plate Ccan have an arc shape. The arc shape of the outer perimeter Oof the first collector plate Ccan match, or be similar to, an outer curvature of the filament. An outer perimeter Oof the second collector plate Chave an arc shape. The arc shape of the outer perimeter Oof the second collector plate Ccan match, or be similar to, an outer curvature of the filament.

An inner perimeter Iof the first collector plate Ccan have an arc shape. The arc shape of the inner perimeter Iof the first collector plate Ccan match, or be similar to, an outer curvature of the filament. An inner perimeterof the second collector plate Ccan have an arc shape. The arc shape of the inner perimeterof the second collector plate Ccan match, or be similar to, an outer curvature of the filament.

As illustrated in, the filament assemblydescribed herein can be used in an x-ray tube. The x-ray tubecan include a cathodeand an anodeelectrically insulated from one another (e.g. by vacuum and by a ceramic or glass tube). The cathodecan include the filament assemblywith the filamentconfigured to emit electrons towards the anode. The filament assemblycan be mounted on a pair of electrodesandand located in a cathode cup. The anodecan include a targetwith a high atomic number material. The targetcan generate x-raysin response to impinging electronsfrom the filament.

A transmission-target x-ray tubeis shown in, with the targeton an x-ray window. The filament assemblydescribed herein is also applicable to reflection-target and side-window x-ray tubes.

As illustrated in, a first electrodeand a second electrodecan each extend from outside the x-ray tubeto an interior of the x-ray tube. A power supply can provide a voltage across the first electrodeand the second electrode, thus causing an electrical current to pass through and heat the filamentso that the filament is capable of being heated by the voltage and the electrical current through the electrical current path.

An electrical current path can be from the first electrodeto and through the first collector plate C, from the first collector plate Cto the first end Eof the filamentand through the filamentto the second end Eof the filament, from the second end Eof the filamentto and through the second collector plate Cto the second electrode.

As illustrated in, the first collector plate Ccan include a first hole Haligned with the first electrode, and the second collector plate Ccan include a second hole Haligned with the second electrode. The first electrodecan be bonded to the first collector plate Cat the first hole Hand the second electrodecan be bonded to the second collector plate Cat the second hole H.

A diameter dof the first hole Hcan be smaller than an outer diameter Dof the first electrode. A diameter dof the second hole Hcan be smaller than an outer diameter Dof the second electrode. Consequently, the first collector plate Ccan rest on top of the first electrodeand the second collector plate Ccan rest on top of the second electrode. This design avoids sharp electrical field gradients that would otherwise result if the electrodesandprotruded through the holes Hand H, respectively.

The first electrodecan span the first hole H. The first electrodecan cover completely an opening of the first hole H. The second electrodecan span the second hole H. The second electrodecan cover completely an opening of the second hole H.

The first collector plate Ccan be welded to the first electrodeat a perimeter of the first hole Hand the second collector plate Ccan be welded to the second electrodeat a perimeter of the second hole H. The weld can be formed by melting an end of the electrodesandnearest to the collector plates Cand C. Therefore, a first connectionbetween the first collector plate Cand the first electrodecan be formed by a portionof the first electrodethat was melted to form the first connection; and a second connectionbetween the second collector plate Cand the second electrodeis formed by a portionof the second electrodethat was melted to form the second connection.

The holes Hand Hallow visual alignment of the filament assemblywith the electrodesand. Welding the filament assemblyto the electrodesandat the holes Hand H, respectively, can be performed at a lower temperature than if the weld were performed without the holes. The holes Hand Hallow visual inspection of the weld after it is completed.

The filament assemblycan be mounted on the pair of electrodesandwithin, at, or in front of an openingof a cathode cup, as illustrated in. The cathode cupcan be associated with the cathode. The planeof the filamentand of the pair of collector plates Cand Ccan be parallel with the openingof the cathode cup.

The filament assemblycan have a slightly smaller diameter than the cathode cupso that the cathode cupforces a central alignment of the filament assembly. This makes manufacturing easier and can result in reduced variation between different x-ray tubes.

A filament can emit electrons in all directions. A planar filament typically emits electrons in a desirable direction, towards the anode target, from a top side of the planar filament that faces the target. The planar filament also can emit electrons in an undesirable direction, towards the cathode cup, from a bottom side of the planar filament. The bottom side is opposite of the top side. The electrons from the bottom side can change direction (e.g. about 180°), due to a negative voltage of the cathode cup, pass between filament wires, and emit towards the target. These electrons from the bottom side are not focused properly. Therefore, the bottom side electrons can result in a misshaped electron spot at the target.

The collector plates Cand Ccan block these electrons emitted from the bottom side, and can keep these electrons within the cathode cup. In order to effectively block such electrons, it is useful for the collector plates Cand Cto block a large percent of the openingof the cathode cupoutside of the filament. For example, the filament assemblycan block ≥70%, ≥80%, ≥90%, or ≥95% of the openingof the cathode cupoutside of the filament.

The collector plates Cand Ccan encircle a large percent of the filamentin order to improve blocking of electrons emitted from the bottom side. For example, the collector plates Cand Ccan encircle a majority of the filament, such as ≥70%, ≥80%, ≥90%, or ≥93% of the filament. As another example, the collector plates Cand Ccan encircle at least 90% of the filament. If the collector plates Cand Cencircle too large of a percent of the filament, then there is risk of the collector plates Cand Ctouching, resulting in a short circuit failure. Therefore, the collector plates Cand Ccan encircle ≤95%, ≤97.5%, or ≤99% of the filament.

In order to allow a voltage across the collector plates Cor Cto cause an electrical current through the filament, it is desirable for no more than one of the collector plates Cor Cto touch the cathode cup. If both collector plates Cand Ctouch the cathode cup, then there would be a short circuit through the cathode cup, and a desired amount of electrical current would not flow through the filament.

In order to avoid this short circuit, the collector plates Cand Ccan have different radii with respect to each other (R1/R2), as illustrated in. For example, R1>R2, where R1 is a largest radius from a centerof the filamentto an outer edge Oof the first collector plate Cand R2 is a largest radius from a centerof the filamentto an outer edge Oof the second collector plate C.

Example relationships between R1 and R2 include the following: R1/R2≥1.01, R1/R2≥1.02, R1/R2≥1.03, or R1/R2≥1.04; and R1/R2≤1.05, R1/R2≤1.1, or R1/R2≤1.2.

An area (A1) of the first collector plate Cis typically larger than an area (A2) the second collector plate C. A larger area (A1) of the first collector plate Ccan allow it to rest on an edge of the cathode cupand support the filament assembly. Example relationships between the area (A1) of the first collector plate Cand the area (A2) the second collector plate Cinclude the following: A1/A2≥1, A1/A2≥3, A1/A2≥5, or A1/A2≥6; and A1/A2≤8, A1/A2≤10, or A1/A2≤15. Both areas A1 and A2 are areas of the side of the first collector plate Cand of the second collector plate Cthat face the target.

The radii R1 and R2 of the collector plates Cand C, respectively, can be substantially larger than a largest radius Rf of the filament, from a centerof the filamentto an outer edgeof the filament. Example relationships between Rf and R1 include the following: R1>Rf, R1/Rf≥1.5, R1/Rf≥2, or R1/Rf≥3; and R1/Rf≤4, R1/Rf≤6, or R1/Rf≤8. Example relationships between Rf and R2 include the following: R2>Rf, R2/Rf≥1.5, R2/Rf≥2, or R2/Rf≥3; and R2/Rf≤4, R2/Rf≤6, or R2/Rf≤8. A purpose of these relationships is to place the filamentin a small area at a center of the cathode cup, but also block nearly all of an area of an openingof the cathode cupoutside of the filament.

is a top-view of a filament groupwith four filament assemblies. During manufacturing, multiple filament assembliescan be connected as shown. A shape of each filament assemblycan be cut in a sheet of metal by laser ablation or by patterning and etching.

The first collector plate Ccan include one, two, three, or more recessed regions() at an outer perimeter. Each recessed regioncan have a tab, extending outward away from the recessed region, for attachment to other filament assembliesin the filament groupduring manufacturing. The recessed regioncan keep the tab, after it is cut, from extending beyond a radius R1 of the first collector plate C. Thus, a largest radiusfrom a centerof the filamentto the recessed regioncan be smaller than a largest radius R1 from a centerof the filamentto an outermost outer edge Oof the first collector plate C. The purpose of this is to keep the tabfrom interfering with placement of the filament assembly in the cathode cup.

Tabson the first collector plate Ccan be sufficient for holding the filament assemblyduring manufacturing. Therefore, the second collector plate Ccan be free of any recessed regions at an outer perimeter thereof. An entire outer perimeter of the second collector plate Ccan have an arc shape.